Indian laterites, and lateritious residues of southern Germany: a petrographic, mineralogical, and geochemical comparison

Borger, H. and Widdowson, M. (2001). Indian laterites, and lateritious residues of southern Germany: a petrographic, mineralogical, and geochemical comparison. Zeitschrift fur Geomorphologie, 45(2) pp. 177–200.

Abstract

The Bohnerz Formation of the Swabian Alb (southern Germany) currently exists as a series of isolated pockets of iron rich pebbles, often pisolitic in nature and typically set within a kaolinitic matrix. These pockets represent infillings of karst solution pits located on the higher elevations of the Swabian Alb. A history of exploitation of the Bohnerze for their iron indicates their existence has long been recognized, however, their origin and evolution has remained a source of debate. Petrographical, mineralogical, and geochemical comparison between the Bohnerz and Indian laterite clearly demonstrates that their origin is consistent with the development of a widespread lateritic weathering residuum in southern Germany during the Cretaceous and early Tertiary. The Bohnerz Formation therefore represents the residues of a palaeo-weathering regime, and the last vestiges of a once extensive tropical weathering surface. Moreover the long term geomorphological evolution of the entire region is best explained in terms of a phase of Late Cretaceous - early Tertiary etchplanation which was terminated by erosion and stripping as a consequence of the climatic change since the later Eocene and early Oligocene. The geomorphology of southern Germany is clearly a landscape palimpsest controlled and influenced by regional tectonics associated with the adjacent Alpine orogeny, by Cretaceous 'greenhouse' conditions, and by dramatic climatic changes at the end Cretaceous and during the Tertiary.

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